In the early stories, the art had Superman's S symbol being smaller than it eventually became, and there being more of a yellow background behind his main S and there was no red outline to the shield. The symbol also looked more like an actual heater-style shield with a simple S drawn on it, rather than the now-iconic diamond-shaped shield and stylized S.
Supergirl originally didn't wear the red skirt which has become part of her iconic look, and she wore her hair short and curly. In the 70's, her hairstyle changed to the wavy and shoulder-length look which she became associated with.
Lex Luthor originally had a full head of red hair, and was sometimes drawn with a pudgy physique.
The first story where Jimmy Olsen gained powers as Elastic Lad, which was included in issue 31, had Jimmy wear a costume that was green instead of magenta and had the writing on his chest include a definite article in his codename by reading "The Elastic Lad" instead of just "Elastic Lad".
Darkseid's debut in issue 134 shows his face on a monitor used by Morgan Edge, depicting him with a white helmet when he is more well-known for wearing blue armor and having a Caucasian skin tone rather than gray. In addition, his eyes used to be more normal-looking before they were eventually changed so that they were colored red and lacked pupils.
The Calvin Ellis Superman (who is President of the United States and comes from a world where the superheroes are predominantly black, being inspired byBarack Obama) was nearly indistinguishable from the regular Superman in his introduction at the end of Final Crisis, with the exceptions of his ethnicity and the colors of his chest insignia being inverted. By issue nine of Action Comics (New 52), he not only follows the standard Superman's omission of Underwear of Power, but is also made more distinguishable by no longer having a spit curl and his costume overall having a more distinct design (particularly the cape and boots).
Batman originally wore short, purple gloves without the iconic three blades on the sides. His original concept art design by Bob Kane was even more drastically different. Batman wore a domino mask instead of a cowl, red tights instead of gray ones, no gloves at all and had two stiff bat wings instead of his jagged cape. Luckily Bill Finger convinced Kane to add all the familiar elements that we've all come to know and love over the years.
Catwoman originally didn't wear a costume, and while she did occasionally wear a mask, it was an actual cat-faced mask as opposed to her better known cowl with cat ears. When she did eventually switch to a proper costume, it was a flamboyant purple outfit (which itself was at first yellow and then green due to inconsistent Golden Age coloring) that included a cape and skirt, a far cry from the black Spy Catsuit most fans tend to associate with her. The purple outfit would be revived decades later for her appearances in the Batman: The Brave and the Bold cartoon as part of the retro throwback visual style.
Dick Grayson's first Nightwing costume was a largely blue outfit with a high disco collar, lovingly dubbed "Discowing" by fans. His more iconic black bodysuit wouldn't be introduced until the 90s.
Jason Todd was actually a redhead Pre-Crisis, and his original Robin costume was a unique design that included a cowl instead of a simple Domino Mask, as well as pants, red boots and long sleeves. This look was quickly done away with due to Crisis on Infinite Earths, which retconned Jason's hair color to black and gave him a copy of the original Robin suit worn by Dick Grayson. However, Grant Morrison's later run reestablished Jason as a redhead, with the original change explained as Jason having dyed his hair at Bruce's behest.
The modern version of Batwoman debuted in the series 52, with a different look than what she'd sport in her ongoing series and Detective Comics appearances. Kate was first depicted as having long auburn-red hair, was more into dresses for her fashion sense, and had brown eyes. Also, while her costume was mostly the same, it also included a pair of red heels. When her series came around, her skin was dramatically lightened to be a "vampire porcelain white" (to better reflect a redhead's complexion), she was depicted as dressing in a more Goth/Punk Rock style (as well as favoring suits over dresses for formal occasions), her hair became short and a highly saturated shade of red, and her eyes were changed to green. Her costume’s heels were also replaced with a set of more practical boots.
Harley Quinn's Gang of Harleys originally all shared her red and black color scheme. Eventually, however, their colors became diversified — while Harley herself keeps her red, Bolly Quinn became orange, Coach became yellow, Harvey Quinn became green, Hanuquinn became blue, Carli Quinn became purple, Harley Queens became pink, and Harlem Harley became white.
Deadshot looked completely different when he first appeared, sporting a tuxedo, top hat and Domino Mask. Needless to say, fans familiar with his iconic costume (which didn't debut until the late 70s) would find him completely unrecognizable here.
Wonder Woman herself had a slightly different costume and hairstyle in her Golden Age adventures, with her outfit including a star-spangled skirt. The skirt later became a pair of shorts, before artists eventually settled on her iconic Leotard of Power.
Hippolyta initially looked nearly exactly like her daughter, before suddenly gaining blond hair during the Silver Age. Since then, artists have gone back and forth on her hair color, with the Post-Crisisrun restoring her black hair, only for the New 52run to make it blond again, with the DC Rebirthrun once again making it black.
Cassie Sandsmark's original Wonder Girl costume included a leather jacket, glasses, kneepads, gloves, and a black wig to hide her blond hair. Cassie herself also had a fairly plain appearance, especially when compared to other superheroines or even Donna Troy, her immediate predecessor. She got Progressively Prettier over time, and would eventually ditch the wig and glasses (as well as the rest of her original outfit) during her tenure with Young Justice.
The original Black Canary wore a Domino Mask early on but it was quickly discarded. Post-Crisis, the mask was mainly used as a way to distinguish between the original Black Canary Dinah Drake and her Legacy Character daughter Dinah Lance.
The android Red Tornado originally had gloves, boots, trunks and a cape that were all colored purple and lacked the T chest insignia (instead having a purple tornado icon on his belt buckle) as well as the yellow arrow on his forehead.
Rick Tyler's first outfit as the second Hourman was drastically different compared to his father's. When he first appeared in Infinity, Inc., he sported a blue outfit with red gloves, leg tassles, and belt, alongside a clock face on his chest and a blue domino mask. When he returned in JSA (1999) during the Stealing Thunder arc, he starts wearing a modernized version of his father's costume.
Kid Flash's costume was initially just a smaller copy of the outfit worn by The Flash. His more unique yellow outfit with the exposed hair was only introduced two years later.
Rather than a mask, Hawkman originally wore a headdress or helmet shaped like the head of a hawk that didn't actually do much to hide his face. He eventually switched to a more standard luchador-like mask with a red hawk insignia on the forehead, which later artists would use to visually distinguish the Earth-2 Hawkman from his Earth-1 counterpart.
Aquaman originally had yellow gloves rather than green. Later artists would use this difference to distinguish between the Golden and Silver Age iterations of the character.
In the Silver Age, Aquaman's Kid Sidekick Aqualad had brown hair instead of black in his earliest appearances.
When Jackson Hyde aka the second Aqualad first debut in Brightest Day, his hair was brown and in a loc-hairstyle. When he returned during DC Rebirth, he bleached his hair blond and grew it out.
Fire from the Justice League International first debuted with a very conservative design that showed almost no skin and even included a mask, a far cry from the more sexy and sensual looks she would later be known for. She was also called "Green Fury" and "Green Flame" in her early appearances, and was only renamed Fire after joining the Justice League.
Green Arrow was originally clean shaven and sported a simpler, far less detailed costume. His iconic design and goatee were not introduced until The '70s, when he adopted a radically new look in the pages of Justice League of America. Funnily enough, most of this came back during the New 52 until it reverted for Green Arrow (Rebirth)
Guy Gardner and John Stewart originally just wore the same standard GL uniform sported by Hal Jordan. It wasn't until The '80s that John and Guy were redesigned and given more unique costumes. John's best known costume didn't even originate in the pages of Green Lantern, as it was actually designed for the 2001 Justice League animated series before making its way to the comics.
The Green Lantern Corps member Ch'p was depicted in his debut in the 148th issue of Green Lantern Vol 2 as a realistically-drawn squirrel in a generic Green Lantern costume. By the mid-1980's, he was redesigned to look more like a Funny Animal and has his costume changed to be closer to appropos apparel, complete with overalls, white gloves and a bowtie.
When Lian Harper was introduced she took after her father, Roy Harper (Speedy/Red Arrow/Arsenal). By the time she was a toddler she had been redesigned to take after her mother Cheshire. Her red hair changed to black and she gained more Asian facial features.
Eclipso looked just like Bruce Gordon at first, but soon gained pointed ears and a more demonic face.
When Beast Boy's origin was first shown in Doom Patrol, he was originally a brunette. When his origin was regiven a few issues later he was shown to be blond. He's been depicted as blond ever since, barring the Young Justice (2010) cartoon where he was a redhead, Teen Titans: Earth One where he was brunet, and DC Super Hero Girls (2019) where he's a brunet. Also, his transformations were drastically different. For his first few appearances in the Doom Patrol he transformed into normal colored animals that had his green, human face on it, rather than just a green animal.
Other Doom Patrol examples.
Rita Farr/Elasti-Girl and Larry Trainor/Negative Man were originally depicted in solid green uniforms, but would start donning the Doom Patrol's more familiar red and white costumes in the 89th issue of the first Doom Patrol series (which was originally titled My Greatest Adventure before rebranded to focus solely on the Doom Patrol at issue 86).
Mento was initially depicted with a yellow costume and a helmet that left the top of his head uncovered before quickly wearing a black costume with only the lightning bolt insignia colored yellow as well as his helmet covering the top of his head completely.
While the Doom Patrol's archenemy the Brain is recognizable from his brain being encased in a skull-shaped container, that wasn't the case for his first appearance in Doom Patrol volume one issue 86, where he was depicted as a generic Brain in a Jar. It wasn't until issue 108 that the Brain was depicted in a container remotely resembling the iconic skull-tank look.
